This application seeks to continue dissection of structure-function relationships of the interaction between LH/hCG and the LH/hCG receptor. Aim 1 concerns analysis of sites on the hormone that contact and activate the receptor, while Aim 2 examines the receptor for sites that contact the hormone. Aim 3 deals with analysis of receptor domains responsible for delivery of the activation signal to either cAMP or IP signalling pathways. The goal is to define, at the amino acid level, the chemical processes by which hCG binds and activates its receptor, leading to activation of two distinct pathways.